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The average cost of female to male reassignment to the NHS is around £30,000 (NZ$55,000).

The cost of egg freezing IVF is around £3,000 more.

One of Britain's leading gender identity experts told the Mail on Sunday that patients undergoing gender reassignment surgery had as much right to preserve their fertility as cancer patients storing eggs or sperm before treatment.

Dr James Barrett, of the NHS Gender Identity Clinic in West London, said three of his patients who have transitioned from women to men were close to becoming parents.

He said that in the last year, he had asked GPs to refer about 50 of his female-to-male patients to have eggs frozen, and about 100 of his male-to-female patients to have sperm frozen.

"As a matter of principle, anybody who loses their fertility as a result of standard NHS treatment should be able to preserve their fertility," he said.

Some local NHS authorities had agreed to fund fertility treatment for his patients immediately, Dr Barrett said. Others refused or took months to decide, he said.

But critics said the NHS should not be spending such sums, at a time when many basic services such as cataract operations are being rationed.

Tory MP Peter Bone said: "I am not sure why the taxpayer should be funding this. I just sometimes ask if the NHS is getting its priorities right."

Most transgender parents who freeze their eggs before fully transitioning from female to male will attempt to have children through a surrogate mother - often the man's partner.

But in 2008 Thomas Beatie caused controversy after becoming pregnant after taking testosterone and surgery to give him a more male appearance.

The former beauty queen, who was born a woman, decided against a hysterectomy and at the age of 34 he conceived his daughter Susan with the help of an anonymous sperm donor.